1. Field of the Invention
This invention relates to camera systems having distance measuring apparatus and more particularly to a camera system having a distance measuring apparatus for automatically focusing.
2. Related Art Statement
Recently, most of the operations in a camera which have been conventionally operated by hand are being automated and accordingly the focusing technique of the camera, that is, the technique of automatically focusing an object hard to focus has been improved. However, the technique of automatically focusing the below described objects, that is,
(1) an object present outside the center of a photographed picture and PA1 (2) a moving object is particularly difficult and has been desired to be improved. PA1 [1] a multi-point distance measuring technique of measuring distances to objects present at a plurality of points within a photographed picture and PA1 [2] a moving object distance measuring technique wherein a distance to an object present at a point within a photographed picture is measured, then the distance to the object present at this point is measured by delaying the time, these measurements are made a plurality of times, on the basis of the results of these distance measurements, the moving speed of the object is detected and thereby the focus lag with the movement of the object as produced during the release time lag is prevented. Regarding the latter moving object distance measuring technique, for example, a detecting apparatus for detecting the speed of a moving object on a belt conveyer is disclosed in the publication of Japanese patent application laid open No. 23257/1987 and an automatic focus adjusting apparatus whereby an automatically focused state can be maintained irrespective of the motion of the object is disclosed in the publication of Japanese patent application laid open No. 159817/1988. PA1 (a) As the multi-point distance measurement is to prevent the intermediate through phenomenon, except in the case that the object in the central part of the photographed picture is at a far distance, the distance measurement on the peripheral part of the photographed picture can be omitted. PA1 (b) In case the object is at a far distance, the object will be able to be covered with the photographed field depth and therefore, even if the object is a moving object, the moving object distance measurement will be able to be omitted. PA1 (c) In the case of following a moving object, the probability of positioning the object in the center of the photographed picture will be so high that, in the moving object distance measurement, the distance measurement in the peripheral part of the photographed picture will be able to be omitted. PA1 (1) The distance of the object substantially in the central part of the photographed picture is measured by the first distance measuring means. PA1 (2) if the result of measuring this distance is a far distance exceeding a predetermined value, the intermediate through phenomenon will be judged to be likely and the distance of the peripheral part will be measured by the second distance measuring means, that is, the multi-point distance will be measured. PA1 (3) On the other hand, if the above mentioned distance measured result does not exceed a predetermined value, that is, is not a far distance, now the moving object distance will be measured.
As conventional technical means for automatically focusing these objects and preventing defocusing, corresponding to the above mentioned respective items (1) and (2), there have been two techniques including:
However, in the above mentioned two techniques, that is, the multi-point distance measuring technique and moving object distance measuring technique, there is a problem that time is taken to measure the distance to the object. That is to say, on the above mentioned paragraph [1], the more the number of points for measuring the distances to the objects, the longer the time required to measure the distances. On the above mentioned paragraph [2], the distance measurement while delaying the time is required a plurality of times and the time required to measure the distance will be long. Therefore, in both of the distance measuring techniques in the above mentioned paragraphs [1] and [2], the release time lag has been likely to be produced.
That is to say, in the camera having the multi-point distance measuring function and moving object distance measuring function, with merely combining these techniques, the release time lag will become long and the precious shutter chance is likely to be missed.